Bring 2 pounds (4 cups) of water to a boil on the stovetop. Add 3¼ ounces salt (that’s about ½ cup Diamond Crystal Kosher Salt, 6 tablespoons Morton’s Kosher Salt, or 5 tablespoons Morton’s Table Salt). Add 1¾ ounces (¼ cup) white sugar and stir until salt and sugar are dissolved. Take the brine off the heat and add 2 pounds (4 heaping cups) ice. Let cool to room temperature, stirring occasionally.
Add 4 onions, chopped coarse; 8 cloves of garlic, smashed; 1 bunch fresh thyme; and 2 big sprigs of fresh rosemary. Note: change this part up as you like it, just make sure to use lots of your flavor ingredients. It’s an inefficient process, so you’ve got to overdo it to make an impact.
Transfer the pork butt and brine into your brining container (or maybe use the pot you cooked the brine in). Cover and refrigerate overnight.
Remove the pork butt from the brine and let sit on a wire rack to drain while you prepare the rub. Mix 2 tablespoons brown sugar with one of the spice mixtures in a small bowl. Rub spice rub all over the pork butt.